Ben Huntington

Modeling and Simulation of a Multilayer Polymer Coextrusion Process

Micro and nano-layered polymer composite materials have a variety of different applications. Very finely layered polymer materials have a large range of technological applications, including optical data storage, lenses, organic lasers, gas barriers, and water purification membranes. All of these applications either require or are greatly enhanced by having flat layers that have controllable thicknesses. These materials are made via a special coextrusion process at Case Western Reserve University that takes an input of a small number of layers (2-8 layers) and then, by splitting and recombining the flow repeatedly, creates a very finely layered material. The multiplying process is depicted in the figure below.

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Figure 1: A multiplier die splits a two layer flow of different polymers and then stacks the flows to create a four layer flow. Figure from Dooley, J.: Viscoelastic Flow Effects in Multilayer Polymer Coextrusion. Ph.D. Thesis, Eindhoven University of Technology (2002).

This process creates many distortions in the layers of fluid, often resulting in the destruction of the layered structure. These flows can be related to the viscous and elastic forces that exist in polymer flows. In flows where the viscosities and/or elasticities are very different, the distortion in the layers can become so extreme that one of the fluids encapsulates one or more of the others, resulting in a material that no longer has the desired properties. These defects and instabilities are seen in Figure 2. The goal of my research is to determine the causes of this distortion and determine ways to negate or circumvent it. My work uses theoretical and computational tools to simulate these flows and their distortions. It serves to augment and guide experimental work being done at Case Western Reserve University.

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Figure 2: A variety of different interface distortion mechanisms are shown. Figure from Simulation and Analysis of Multiphase and Stability of Coextruded Layered Polymeric Films M.S. Thesis, Chabert, E., University of Texas at Austin (2011)